(i) Field of the Invention
This invention relates to an ignition source for internal combustion engines.
(ii) Description of the Prior Art
The internal combustion engine is required to operate and to burn fuel efficiently over a wide range of speed and load requirements. This is normally achieved by using a rich mixture which burns evenly during the power cycle. Although a rich mixture gives the engine good performance characteristics it is wasteful of fuel and produces a high level of pollutants. A mixture which provides sufficient air to consume all of the fuel charge is too lean for optimum performance and this is particularly true of slow burning fuels, e.g., methane (natural gas).
Research has been progressing to find a means of igniting lean mixtures in such a way that the burn can be completed evenly and quickly.
One method which has been proposed is typified in Canadian Pat. No. 429,758 which involved swirling air around the interior of the engine combustion chamber during the piston compression stroke at a controlled rate with respect to the engine speed. Fuel is then injected under pressure into the air charge during each cycle of operation of the engine. During each cycle of engine operation, a patch of combustible mixture is progressively formed and consumed in a localized area in the combustion chamber. As a result, it was alleged that little or no combustible "end" gases were permitted to exist, and that "ping" or "knock" was inhibited even with fuels with low anti-knock value at high compression rates.
Barber, Canadian Pat. No. 565,196 issued Oct. 28, 1958, provided an improvement by injecting fuel in the form of a spray into the combustion chamber from a particular point and aimed in a particular direction. This was alleged to provide an improved combustion environment.
U.S. Pat. No. 2,184,009 issued Oct. 11, 1949, provided another improvement by the positioning of the ignition means very much closer to the fuel injection means than had been done previously, allegedly resulting in the ignition of fuel-air mixture sooner, and in the use of a wider range of spray shapes to produce knock-free operation regularly.
Barber, Canadian Pat. No. 588,190 issued Dec. 1, 1959, provided still another improvement by the use of a particularly defined fuel injection means including a nozzle body, an orifice plate with valve seat and a slidable valve for cooperating with the orifice plate to control the fuel flow through the orifice.
Barber et al. Canadian Pat. No. 981,998 issued Jan. 20, 1976, provided an improvement by using a fuel-air charge, which had been premixed in proportions to provide a mixture capable of flame ignition, but incapable of spark ignition. The premixed fuel-air charge was caused to flow rapidly about the combustion chamber in a swirling pattern, and a pilot charge of fuel was injected into the swirling premixed charge, thereby to form a spark-ignitable fuel-air mixing surrounding the spark plug. Ignition of the spark-ignitable mixture by the spark plug establishes a flame further to ignite the fuel-air mixture swirling within the combustion chamber.
Thus, these Barber patents embody the single concept of non-turbulent liquid pilot injection directly into the combustion chamber in the vicinity of the spark. Turbulence is generated separately by the intake stroke. The Barber patents require extensive combustion chamber modifications and are intended for liquid fuels.
Other proposals have been made to improve the combustion efficiency through the generation of turbulent conditions within the engine cylinder In Canadian Pat. No. 848,750 issued Aug. 11, 1970 to Daimler-Benz, an eddying or whirling movement is imparted to the inflowing fuel-air about an axis extending in the longitudinal direction of the cylinder. That eddy or vortex is then displaced in the compression top-dead-centre position into the piston combustion chamber. This was alleged to provide an extension of the knocking limit by about two compression units. This was alleged to provide somewhat lower fuel consumption and to use a less expensive fuel of a lower octane ratio at the usual compression ratio heretofore common.
Canadian Pat. No. 869,305 issued Apr. 27, 1971 to American Gas Association, the turbulent conditions are embodied in a scavenging air flow coupled with a predetermined position of the glow plug in the combustion chamber.
Canadian Pat. No. 887,977 issued Dec. 14, 1971 to Dynatech Corporation, involves the jetting of hot gas into the cylinder to penetrate and ignite the fuel-air mixture.
U.S. Pat. No. 3,107,658 issued Oct. 22, 1963 to S. Meurer provides for injecting fuel onto the wall of the cylinder, and then forming a unidirectional air swirl therein to mix air with the fuel and means to inject particles of fuel towards the igniting device.
U.S. Pat. No. 3,534,714 issued Oct. 20, 1970 to A. Urlaub provides a fuel injection nozzle means, an intensive air swirl generating means and an anode electrode, with the wall of the cylinder forming the cathode.
U.S. Pat. No. 4,133,322 issued Jan. 9, 1979 to Mitsubishi provides for the injection of air towards the spark gap to create a swirl or turbulence to increase combustibility.
U.S. Pat. No. 4,176,649 issued Dec. 4, 1979 to Toyota provides for compressing the air-fuel mixture in the cylinder to cause turbulence and swirling in the auxiliary section of the combustion chamber to control the rate of combustion.
Thus, in these prior patents as well, extensive combustion chamber modifications are necessary.
Other proposals which have been made are those which involve a stratified fuel charge or a pilot flame.
Thus, Canadian Pat. No. 537,727 issued Mar. 5, 1957 to Daimler-Benz provides fuel injection system which injects a compact jet of fuel into the pre-combustion chamber.
Canadian Pat. No. 994,627 issued Aug. 10, 1976 to Honda provides a main combustion chamber and an auxiliary chamber. The rich mixture fed to the auxiliary chamber is ignited by a spark plug and this causes the lean mixture in the main combustion chamber to be ignited.
Canadian Pat. No. 1,020,423 issued Nov. 8, 1977 to Honda provides an improvement on Canadian Pat. No. 994,627 by recycling exhaust gases through the auxiliary combustion chamber to reduce NO.sub.x fumes.
Canadian Pat. No. 1,092,458 issued Dec. 30, 1980 to Fiat provides an insert in the cylinder providing an ignition pre-chamber to ignite fuel injected into the cylinder which has been finely atomized by impingement on an impingement surface.
Kamiya, U.S. Pat. No. 4,091,774 patented May 30, 1978, provides a stratified combustion-type engine in which an injection nozzle injects auxiliary fuel towards the combustion chamber. An open pre-combustion chamber equipped with a spark plug locally holds and vaporizes the auxiliary fuel to increase its burning rate while a lean mixture also admitted to the combustion chamber is ignited by the flame of the rich mixture.
Thus, these proposals provide a liquid fuel pilot injection system which relies on combustion to generate turbulence and flame for further combustion. While most proposals are "add on" devices, they do require additional pre-combustion chambers and are designed for use with liquid fuels.
Other patents purported to provide improved combustion by providing spark plugs having corona discharge or high energy spark characteristics. Among them are Canadian Pat. No. 1,044,973 issued Dec. 12, 1978 to Tokai TRW & Co. Ltd.; U.S. Pat. No. 4,041,922 issued Aug. 16, 1977 to Tokai TRW & Co. Ltd.; U.S. Pat. No. 4,124,003 issued Nov. 7, 1978 to Tokai TRW & Co. Ltd.; U.S. Pat. No. 4,219,001 issued Aug. 26, 1980 to Tokai TRW & Co. Ltd.; and U.S. Pat. No. 4,317,068 issued Feb. 23, 1982 to Combustion Electromagnetics Inc.
Plasma jet ignition is one method which has been developed in an attempt to achieve this goal. One example of such proposal is in U.S. Pat. No. 4,164,912 issued Aug. 21, 1979 to R. R. C. Baylor. A comparatively large amount of electrical energy is released into a cavity causing a jet of highly excited gas to be shot into the cylinder. This plasma plume causes ignition of a lean mixture at many sites and gives a satisfactory power burn. Unfortunately the energy consumption and electrode wear of this system is prohibitive and until now these drawbacks had not been resolved.